1. Technical Field
The present invention is related to a rubber composition for use in tire treads.
2. Related Art
Rubber compositions for use in tire treads including a terminal-modified vinyl aromatic-diene copolymer and an emulsion polymerized styrene-butadiene copolymer rubber and/or a solution polymerized styrene-butadiene copolymer rubber are known as rubber compositions for use in treads of tires for use in high-speed running (Japanese Unexamined Patent Application No. H06-65418).
Additionally, compounding a diene rubber with silica and using a modified diene rubber in which a substituent having affinity with silica has been introduced as the diene rubber is also known. For example, a rubber composition is described in Japanese Patent No. 3488926 that includes a hydroxy group-containing diene rubber and silica. A rubber composition highly compounded with silica including a terminal hydroxy-modified solution polymerized styrene-butadiene copolymer is described in Japanese Unexamined Patent Application Publication No. 2008-056907.
Additionally, silica is being developed in a variety of ways for use as a filler in polymer compositions. A silica having a particular CTAB (cetyltrimethyl ammonium bromide) specific surface area, a particular BET (Brunauer, Emmett and Teller) specific surface area, a particular physical dimension distribution width, and a particular pore volume distribution is described in Japanese Unexamined Patent Application Publication (translation of PCT application) No. 2005-500238. Using a diene rubber composition including a silica having a particular BET specific surface area, a particular CTAB specific surface area, a particular average particle size, and a particular particle size distribution, porosity, or amount of silanol in the manufacturing of treads for tires for the purposes of reducing rolling resistance and improving abrasion resistance of tires is described in Japanese Unexamined Patent Application Publication (translation of PCT application) No. 2005-500420.
In the development of summer tires for use in Europe, stability when changing lanes during extremely high-speed running such as on the Autobahn is an important factor. Therefore, the development of a tire with superior steering stability during high-speed running is of importance. Additionally, demand for environmental friendly tires that are fuel efficient has increased year by year.
Generally, in order to improve steering stability it has been necessary to provide tires with a high degree of hardness, but compounding large amounts of a filler in order to achieve such high degree of hardness leads to a sacrifice in fuel consumption performance. On the other hand, when an amount of a softener is reduced to ensure a high degree of hardness while a compounded amount of the filler is reduced to ensure fuel consumption performance, it becomes difficult to achieve both fuel consumption performance and mixing processability.